Electrosurgical generator and system

Abstract

An electrosurgical system has an electrosurgical generator with a multiple-phase RF output stage coupled to a multiple-electrode electrosurgical instrument. The instrument has three treatment electrodes each of which is coupled to a respective generator output driven from, for instance, a three-phase output transformer. Continuous RF output voltage waveforms are simultaneously delivered to respective generator outputs at the operating frequency, each waveform being phase-displaced with respect to the other waveforms. The magnitude of the RF output voltage waveform delivered to at least one of the generator outputs is sufficient to cause tissue vaporization at the respective treatment electrodes when the system is used for tissue treatment. Also disclosed is an electrosurgical generator in which the output transformer has windings forming at least three phases, the transformer core being constructed to provide at least three magnetic circuits each of which is inductively linked to the windings of at least two of the three phases.

1. An electrosurgical system comprising:
 an electrosurgical generator for generating radio frequency (RF) power at a generator operating frequency, and 
 an electrosurgical instrument coupled to the generator, 
 the generator comprising a single source of RF power with a multiple-phase RF output stage having at least three outputs for coupling to respective electrodes of the electrosurgical instrument for delivering RF power to the electrodes, the configuration of the output stage being such that respective continuous RF output voltage waveforms are simultaneously delivered across respective pairs of said three generator outputs at the operating frequency, each such waveform being phase-displaced between 10°-170° with respect to the waveforms delivered across the respective other pairs of the three outputs, 
 the electrosurgical instrument comprising at least three treatment electrodes, each treatment electrode being coupled to a respective one of the generator outputs for receiving RF power from the output stage of the generator, and 
 the generator being constructed and arranged, such that the magnitude of the RF output voltage waveforms delivered to at least first and second pairs of said generator outputs being sufficient to allow simultaneous tissue cutting and coagulation at the respective treatment electrodes connected to the first and second pairs of said generator outputs when the system is used for tissue treatment. 
 
     
     
       2. The system according to  claim 1 , wherein the phase displacement of the waveform delivered across each said respective pair of generator outputs with respect to the waveforms delivered across said other output pairs is substantially 120° in each case. 
     
     
       3. The system according to  claim 1 , wherein the system output stage has first, second and third outputs respectively and is configured such that the ratio of (a) the magnitude of each of the RF output voltage waveforms delivered between the first and the second outputs and between the first and the third outputs, and (b) the magnitude of the RF output voltage waveform delivered across the second and the third outputs, is between 2 and 6. 
     
     
       4. The system according to  claim 3 , wherein the generator output stage has a fourth output constituting a neutral output, and is configured such that the phase displacement of the three RF output voltage waveforms delivered between each of the first, second and third outputs respectively and the fourth output with respect to each other is substantially 120°. 
     
     
       5. The system according to  claim 3 , wherein the instrument has a tissue-cutting electrode coupled to the first output of the generator and a pair of coagulation electrodes coupled to the second and third outputs of the generator respectively. 
     
     
       6. The system according to  claim 5 , wherein:
 the generator output stage comprises: a multiple phase output transformer including first, second and third phases each having a primary winding and a secondary winding, the phases being magnetically linked; and a drive circuit coupled to the primary windings for feeding time-varying mutually phase-displaced drive currents through the primary windings; 
 the secondary windings of the first, second and third phases are star-connected so as to have a common, neutral node and are coupled to the cutting electrode and the coagulating electrodes respectively; 
 the secondary winding of the first phase has a greater number of turns than each of those of the second and third phases so that when substantially equal drive currents are fed through the primary windings, the RF voltage developed between the cutting electrode and at least one of the coagulating electrodes is greater than that simultaneously developed between the coagulating electrodes. 
 
     
     
       7. The system according to  claim 6 , wherein the neutral node is connected to a return pad separate from the instrument. 
     
     
       8. The system according to  claim 5 , wherein:
 the generator output stage comprises: a multiple phase output transformer including first, second and third phases each having a primary winding and a secondary winding, the phases being magnetically linked; and a drive circuit coupled to the primary windings for feeding time-varying mutually phase-displaced drive currents through the primary windings; 
 the secondary windings of the first, second and third phases are delta-connected, the cutting electrode is coupled to the junction of the secondary windings of the first and second phases, and the coagulating electrodes are coupled to the junctions of the second and third phase secondary windings and of the third and first phase secondary windings respectively; 
 the first and second phase secondary windings each have a greater number of turns than the third phase secondary winding so that when substantially equal drive currents are fed through the primary windings, the RF voltage developed between the cutting electrode and at least one of the coagulating electrodes is greater than that simultaneously developed between the coagulating electrodes. 
 
     
     
       9. The system according to  claim 1 , wherein the magnitude of the RF output voltage waveform delivered across at least one pair of said three generator outputs is greater than 250 volts RMS and the magnitude of the RF output voltage waveform delivered simultaneously across another pair of said three generator outputs is less than 170 volts RMS. 
     
     
       10. The system according to  claim 1 , wherein the generator output stage comprises: a multiple-phase output transformer, each phase having a primary winding and a secondary winding, the phases being magnetically linked; and a drive circuit coupled to the primary windings for feeding time-varying mutually phase-displaced drive currents to the primary windings. 
     
     
       11. The system according to  claim 10 , wherein the generator operating frequency is at least 75 kHz and the transformer is a three-phase transformer, the secondary windings having ends forming said outputs, and wherein the windings of the three phases share a common transformer core. 
     
     
       12. The system according to  claim 10 , wherein the transformer has a ferrite core. 
     
     
       13. The system according to  claim 12 , wherein the transformer core includes a monolithic ferrite core member having at least three limbs each carrying at least one winding, and an interconnecting bridge magnetically connecting the limbs, said three limbs being of substantially equal cross-section. 
     
     
       14. The system according to  claim 13 , wherein the switching devices of the generator are arranged in pairs, each pair comprising a first transistor and a second transistor connected in series between opposite polarity supply rails of the DC power supply and having a common connection coupled to one end of a respective primary winding, the control circuit being configured to feed control pulses to the first and second transistors so as to drive them in opposition at the operating frequency. 
     
     
       15. The system according to  claim 12 , wherein the transformer core comprises three independent magnetic circuits each carrying the windings of two phases, the windings of each phase being wound around two of the three independent magnetic circuits. 
     
     
       16. The system according to  claim 15 , wherein the generator control circuit is configured to vary the widths of the control pulses, thereby to vary the amplitude of the alternating currents fed through the primary windings. 
     
     
       17. The system according to  claim 10 , wherein the generator drive circuit comprises a plurality of semiconductor switching devices coupled to a DC power supply and the primary windings, the generator output stage including, in each phase, a respective resonant circuit connected to at least one of the switching devices and to the primary winding associated with that phase, wherein the generator further comprises a control circuit connected to the switching devices, the control circuit and the switching devices being constructed and arranged such that control pulses are fed to the switching devices at a predetermined repetition rate to drive the switching devices alternately to conducting and non-conducting states in a phase-displaced sequence thereby to cause alternating currents to be fed through the primary windings at the generator operating frequency, the current in each primary winding being correspondingly phase-displaced with respect to the currents in the other primary windings, and wherein the resonant circuits are resonant at the generator operating frequency. 
     
     
       18. The system according to  claim 17 , wherein the generator control circuit is arranged to drive the switching devices in a 120° phase-displaced sequence. 
     
     
       19. The system according to  claim 10 , wherein the secondary windings have different numbers of turns in order that the RF output voltage developed across at least one pair of the outputs is higher than that developed across another pair of the outputs. 
     
     
       20. The system according to  claim 1 , wherein the generator is constructed and arranged such that the magnitude of the RF output voltage waveform delivered simultaneously to another pair of said generator outputs is insufficient to cause tissue vaporisation but sufficient to cause tissue coagulation at the electrodes coupled to said another pair of outputs. 
     
     
       21. The system according to  claim 1 , wherein the instrument has first, second and third electrodes, the first electrode being a tissue-cutting electrode and the second and third electrodes being tissue-coagulation electrodes. 
     
     
       22. An electrosurgical generator for generating radio frequency (RF) power at a generator operating frequency, the generator comprising:
 a single source of RF power with a multiple-phase RF output stage having at least three outputs for coupling to respective electrodes of an electrosurgical instrument for delivering RF power to the electrodes, the configuration of the output stage being such that respective RF output voltage waveforms are simultaneously delivered across each pair of the said three outputs at the operating frequency, each such waveform being phase-displaced between 10°-170° with respect to the waveforms delivered across the respective other pairs of the three outputs, the RF output voltage waveforms delivered to at least first and second pairs of said three outputs allowing simultaneous tissue cutting and coagulation at respective electrodes connected to the first and second pairs of said three outputs, when the electrosurgical instrument is used for tissue treatment; 
 the output stage comprising a multiple-phase output transformer which has windings forming at least three phases and a transformer core including at least one ferrite core member; and 
 the transformer being constructed to provide at least three magnetic circuits, each magnetic circuit being inductively linked to the windings of at least two of the three phases. 
 
     
     
       23. The generator according to  claim 22 , wherein the transformer core includes a monolithic ferrite core member having at least three limbs each carrying at least one winding, and an interconnecting bridge magnetically connecting the limbs, the said three limbs being of substantially equal cross-section. 
     
     
       24. The generator according to  claim 22 , wherein the transformer core comprises three independent magnetic circuits each carrying the windings of two phases, the windings of each phase being wound around two of the three independent magnetic circuits. 
     
     
       25. The generator according to  claim 24 , wherein the transformer core comprises three annular core members respectively forming the said independent magnetic circuits. 
     
     
       26. An electrosurgical generator for generating radio frequency (RF) power at a generator operating frequency, the generator comprising:
 a single source of RF power with a multiple-phase RF output stage having at least three outputs for coupling to respective electrodes of an electrosurgical instrument for delivering RF power to the electrodes, the configuration of the output stage being such that respective RF output voltage waveforms are simultaneously delivered across each pair of said three outputs at the operating frequency, each such waveform being phase-displaced between 10°-170° with respect to the waveforms delivered across the respective other pairs of the three outputs, the RF output voltage waveforms delivered to at least first and second pairs of said three outputs allowing simultaneous tissue cutting and coagulation at respective electrodes connected to the first and second pairs of said three outputs, when the electrosurgical instrument is used for tissue treatment, 
 the output stage comprising: a multiple-phase output transformer, each phase having a primary winding and a secondary winding, the phases being magnetically linked; and a drive circuit coupled to the primary windings for feeding time-varying mutually phase-displaced drive currents to the primary windings, and 
 the transformer comprising a core which includes a monolithic ferrite core member having at least three limbs each carrying at least one winding, and an interconnecting bridge magnetically connecting the limbs, said three limbs being of substantially equal cross-section. 
 
     
     
       27. An electrosurgical generator for generating radio frequency (RF) power at a generator operating frequency, the generator comprising:
 a single source of RF power with a multiple-phase RF output stage having at least three outputs for coupling to respective electrodes of an electrosurgical instrument for delivering RF power to the electrodes, the configuration of the output stage being such that continuous RF output voltage waveforms are simultaneously delivered across respective pairs of said three outputs at the operating frequency, each such waveform being phase-displaced between 10°-170° with respect to the waveforms delivered across the respective other pairs of the three outputs, the RF output voltage waveforms delivered to at least first and second pairs of said three outputs allowing simultaneous tissue cutting and coagulation at respective electrodes connected to the first and second pairs of said three outputs, when the electrosurgical instrument is used for tissue treatment, 
 the output stage comprising: a multiple-phase output transformer, each phase having a primary winding and a secondary winding, the phases being magnetically linked; and a drive circuit coupled to the primary windings for feeding time-varying mutually phase-displaced drive currents to the primary windings, and
 the transformer core comprising three independent magnetic circuits, each carrying the windings of two phases, the windings of each phase being wound around two of the three independent magnetic circuits.